A private intelligence dossier containing false and salacious claims about President Trump took center stage on Thursday during testimony by fired FBI director James Comey, who revealed the document drove the FBI's counterspy probe into alleged Russian collusion with the Trump presidential campaign.

Comey testified under oath before the Senate Select Committee on Intelligence that Trump asked him to drop an FBI investigation into his former national security adviser, Michael Flynn, something he regarded as an attempt to interfere with the probe.

The former FBI director also revealed that Obama administration Attorney General Loretta Lynch directed Comey in the summer of 2016 not to call the FBI's criminal probe of Hillary Clinton's private email system an investigation.

Lynch instead told him to use the politically safe term "matter," a request Comey said "confused me and concerned me."

Comey said as a result of Lynch's inappropriate contacts during the Clinton probe he considered calling for the appointment of a special counsel to investigate the email system because of Lynch's conflict of interest for meeting Clinton's husband, former President Bill Clinton, during the investigation. But he opposed further investigation because he felt the FBI probe was sufficient.

Comey announced in July that Clinton had been careless in handling highly classified information in private emails but opposed prosecuting her, despite federal laws making the mishandling of classified information a crime.

President Trump did not initially comment on the Comey hearing, but on Friday tweeted, "Despite so many false statements and lies, total and complete vindication…and WOW, Comey is a leaker!" His lawyer issued a statement denying Comey's charges of interfering with FBI probes, and accused him leaking confidential information.

On the dossier, Comey testified that the allegations contained in the 36-page intelligence report, produced by former British spy Christopher Steele for the Washington investigative firm Fusion GPS, had raised concerns the president was being blackmailed by the Kremlin.

Many of the claims in the Steele dossier have been exposed as false, including charges that Trump was compromised by prostitutes working for the FSB intelligence service at a Moscow hotel.

"If the FBI receives a credible allegation that there is some effort to coopt, coerce, direct, employ covertly an American on behalf of the foreign power, that's the basis on which a counterintelligence investigation is opened," Comey said when asked if the document had raised blackmail concerns.

However, when Committee Chairman Sen. Richard Burr (R., N.C.) asked Comey to comment directly on the dossier that the chairman described as "100 percent directed at the president-elect," he declined to comment.

Asked if he believes Trump colluded with Russia, Comey said: "That's a question I don't think I should answer in an open setting. As I said, when I left, we did not have an investigation focused on President Trump. But that's a question that'll be answered by the investigation, I think."

The testimony by the former FBI chief on the dossier followed earlier testimony suggesting a politically motivated campaign was underway by Democrats and other Trump opponents during the presidential race to portray Trump and his aides as tools of Moscow.

Last month, former CIA Director John Brennan, an Obama loyalist, testified to Congress that he asked the FBI, during the height of the presidential campaign, to investigate whether the Trump campaign colluded with Russians.

The House intelligence committee is also investigating whether Obama officials were engaged in a political spying operation against Trump and his transition team using foreign intelligence collection as cover.

Trump's personal lawyer, Marc Kasowitz, issued a statement saying Comey confirmed what he told the president in private that he was not under investigation in the Russian probe.

On Comey's assertion that Trump pressed him to end the Flynn investigation, Kasowitz said "the president never in form or substance directed or suggested that Mr. Comey stop investigating anyone, including the president never suggested that Mr. Comey, quote, ‘Let Flynn go.'"

Kasowitz also denied Trump sought Comey's loyalty. He then accused the former FBI chief of being one of the people he said is currently undermining his administration by "selective and illegal leaks of classified information and privileged communications."

"Mr. Comey has now admitted that he is one of these leakers," Kasowitz said. "Today, Mr. Comey admitted that he unilaterally and surreptitiously made unauthorized disclosures to the press of privileged communications with the president."

The lawyer was referring to conversations between Trump and Comey between January and March that were published in the press.

"Mr. Comey also testified that immediately after he was terminated, he authorized his friends to leak the contents of [personal] memos to the press in order to, in Mr. Comey's words, quote, ‘prompt the appointment of a special counsel.'"

"We will leave it to the appropriate authorities to determine whether these leaks should be investigated along with all the others that are being investigated," Kasowitz said, adding "the president feels completely vindicated and is eager to continue moving forward with his agenda, with the business of this country, and with this public cloud removed."

Comey answered questions from senators for more than two hours and made clear that he not only disagreed with Trump's accounts of his firing but that he believed the president lied when he said the FBI under his watch had been mismanaged.

Trump abruptly fired Comey May 8, initially asserting he had overstepped his authority in seeking to dismiss any prosecution of Clinton, a decision for the Justice Department and not the law enforcement agency. Later in a television interview, Trump said the dismissal was prompted by Comey's handling of the Russian investigation.

Comey testified that Trump wanted the Russia counterintelligence probe ended because it had created a cloud over his administration and was preventing the new president from advancing his policy agenda.

The focus of the hearing quickly shifted from Russian election meddling to Comey's conversations with Trump. They included nine one-on-one conversations over four months, including three in person and six on the phone.

The first meeting between Trump and Comey took place Jan. 6 at Trump Tower in New York. During the meeting, Comey said he was chosen from other intelligence chiefs to inform the president about "salacious and unverified" information about to be published in the press.

He was apparently referring to the questionable Steele dossier that was published four days later by BuzzFeed.

Comey said he wanted to notify Trump about the information, noting, "to the extent there was some effort to compromise an incoming president, we could blunt any such effort with a defensive briefing."

Trump called the allegations in the dossier false and "disgusting" and in several conversations with Comey urged him to publicly announce he was not under investigation.

Democrats at the hearing focused on Comey's conversation with Trump in the Oval Office on Feb. 14.

Comey testified Trump told him regarding the investigation of Flynn, "I hope you can see your way clear to letting this go, to letting Flynn go. He is a good guy. I hope you can let this go."

"Gen. Flynn, at that point in time, was in legal jeopardy," Comey said. "There was an open FBI criminal investigation of his statements in connection with the Russian contacts and the contacts themselves. And so that was my assessment at the time."

Republican Sen. James Risch (Idaho) asked Comey whether he knew of anyone who had been prosecuted for obstruction of justice for saying they hoped an investigation would end.

Comey said he was unaware of any prosecutions based on that statement.

On the question of whether Trump had sought to obstruct justice, a crime, Comey said: "I don't think it's for me to say whether the conversation I had with the president was an effort to obstruct. I took it as a very disturbing thing, very concerning, but that's a conclusion I'm sure the special counsel will work towards, to try and understand what the intention was there, and whether that's an offense."

Former FBI Director Robert Mueller was appointed a special counsel for the Russia investigation and has launched a parallel probe to those in the Senate and House.

After the hearing, Sen. Marco Rubio (R., Fla.) said he did not hear anything during the hearing that placed the president in legal jeopardy. "I didn't hear anything today that pointed to that," Rubio said.

Comey again sought to defend his public exoneration of Clinton during the hearing noting that the painful decision he made would protect the FBI from accusations of political meddling in the election.

The former FBI chief testified that during one meeting with Trump the president asked for his loyalty saying he "needed loyalty" from him. Comey said he promised honesty and then said the two men agreed he would provide "honest loyalty."

Comey said he was confused by his firing because Trump had told him he was doing a great job and that he would stay during his administration.

"So it confused me when I saw on television the president saying that he actually fired me because of the Russia investigation and learned, again from the media, that he was telling, privately, other parties that my firing had relieved great pressure on the Russia investigation," he said.

Administration statements that the FBI was "in disarray," poorly led, and that the workforce had lost confidence him were false, Comey said.

"Those were lies, plain and simple, and I am so sorry that the FBI workforce had to hear them and I'm so sorry that the American people were told them," Comey said.

FBI sources have said many field agents were upset by Comey's handling of the Clinton email investigation that undermined the Bureau's integrity.

"I have a message before I close for the—my former colleagues at the FBI," Comey said. "But first, I want the American people to know this truth: The FBI is honest. The FBI is strong. And the FBI is, and always will be, independent."

The FBI has come under fire for mishandling several major terrorism investigations, including investigations of terrorists who carried out the mass shootings in San Bernardino and Orlando.

Update June 9, 9:10 a.m.: This post has been updated to include President Trump's tweet on Friday morning.